A resistance-change semiconductor memory is a semiconductor memory which uses a resistive memory element as a recording medium. The resistive memory element is an element formed of a material whose resistance varies in response to voltage, current, heat and other factors. Magnetoresistive random access memory (MRAM), phase-change random access memory (PCRAM) and resistive random access memory (ReRAM) are all varieties of resistance-change semiconductor memory which are expected to be deployed as high-capacity, high-speed next-generation semiconductor memories.
As a memory cell of the resistance-change semiconductor memory, a cross point type, a one-transistor/one-memory-element type or a two-transistor/one-memory-element type have been investigated in terms of reduction in cell area, improvement in operating characteristics and other factors.
The cross point type is mainly adopted in the ReRAM and the PCRAM and has a single structure where each memory cell is arranged at the intersection of two conductive lines, which is effective for reducing the cell area. However, there is a reduction in selectivity (operating characteristics) of the memory cells because of sneak current.
The one-transistor/one-memory-element type and the two-transistor/one-memory-element type are mainly adopted in the MRAM, and they are effective for improving the selectivity of memory cells. However, a transistor must be provided in each memory cell, and hence an increase in cell area is inconvenient as compared with the cross point type.
In a so-called a spin torque transfer MRAM that executes magnetization reversal by using a polarized spin current in particular, both a write operation and a read operation are executed by passing a current through each memory cell. Therefore, to reduce a probability of destruction of stored information due to a so-called disturbance, it is important to provide a transistor in each memory cell to enhance the selectivity of the cells. However, as described above, there is a problem that the cell area increases in comparison with the cross point type.